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Digital Transmission & Analog Transmission. 1. DIGITAL-TO-DIGITAL CONVERSION. Digital Data -> Digital Signal Three techniques: line coding ( always needed ) block coding (working with NRZ-I) Scrambling (working with AMI). Figure 4.1 Line coding and decoding.

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Digital transmission analog transmission

Digital Transmission&Analog Transmission


1. DIGITAL-TO-DIGITAL CONVERSION

  • Digital Data -> Digital Signal

  • Three techniques:

    • line coding (always needed)

    • block coding (working with NRZ-I)

    • Scrambling (working with AMI)

4.#


Figure 4.1 Line coding and decoding


Figure 4.2 Signal element versus data element

r = number of data elements / number of signal elements


  • Data Rate Vs. Signal Rate

    • Data rate: the number of data elements (bits) sent in 1s (bps). It’s also called the bit rate

    • Signal rate: the number of signal elements sent in 1s (baud). It’s also called the pulse rate, the modulation rate, or the baud rate.

  • We wish to:

  • 1. increase the data rate (increase the speed of transmission)

  • 2. decrease the signal rate (decrease the bandwidth requirement)

    • Worst case, best case, and average case of r

    • S = c * N / r baud


Baseline wandering

Baseline: running average of the received signal power

DC Components

Constant digital signal creates low frequencies

Self-synchronization

Receiver Setting the clock matching the sender’s


Figure 4.4 Line coding schemes


Figure 4.5 Unipolar NRZ scheme


Figure 4.6 Polar NRZ-L and NRZ-I schemes


Figure 4.7 Polar RZ scheme


Figure 4.8 Polar biphase: Manchester and differential Manchester schemes


  • High=0, Low=1

  • No change at begin=0, Change at begin=1

  • H-to-L=0, L-to-H=1

  • Change at begin=0, No change at begin=1


Figure 4.9 Bipolar schemes: AMI (Alternate Mark Inversion) and pseudoternary


Multilevel Schemes

  • In mBnL schemes, a pattern of m data elements is encoded as a pattern of n signal elements in which 2m ≤ Ln

  • m: the length of the binary pattern

  • B: binary data

  • n: the length of the signal pattern

  • L: number of levels in the signaling


Figure 4.10 Multilevel: 2B1Q scheme


Figure 4.13 Multitransition: MLT-3 scheme


Table 4.1 Summary of line coding schemes

Polar


Block Coding

  • Redundancy is needed to ensure synchronization and to provide error detecting

  • Block coding is normally referred to as mB/nB coding

  • it replaces each m-bit group with an n-bit group

  • m < n


Figure 4.15 Using block coding 4B/5B with NRZ-I line coding scheme


Figure 4.14 Block coding concept


Table 4.2 4B/5B mapping codes


Scrambling

  • It modifies the bipolar AMI encoding (no DC component, but having the problem of synchronization)

  • It does not increase the number of bits

  • It provides synchronization

  • It uses some specific form of bits to replace a sequence of 0s


Figure 4.19 Two cases of B8ZS scrambling technique

B8ZS substitutes eight consecutive zeros with 000VB0VB


Figure 4.20 Different situations in HDB3 scrambling technique

HDB3 substitutes four consecutive zeros with 000V or B00V depending

on the number of nonzero pulses after the last substitution.


2. ANALOG-TO-DIGITAL CONVERSION

  • The tendency today is to change an analog signal to

  • digital data.

    • pulse code modulation

    • delta modulation.


Figure 4.21 Components of PCM encoder


According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency contained in the signal.

What can we get from this:

1. we can sample a signal only if the signal is

band-limited

2. the sampling rate must be at least 2 times the highest frequency, not the bandwidth


Figure 4.26 at least 2 times the highest frequency contained in the signal.Quantization and encoding of a sampled signal


Contribution of the at least 2 times the highest frequency contained in the signal.quantization error to SNRdb

SNRdb= 6.02nb + 1.76 dB

nb: bits per sample

(related to the number of level L)

The minimum bandwidth of the digital signal is nb times greater than the bandwidth of the analog signal.

Bmin= nb x Banalog


DM at least 2 times the highest frequency contained in the signal. (delta modulation) finds the change from the previous sample

Next bit is 1, if amplitude of the analog signal is larger

Next bit is 0, if amplitude of the analog signal is smaller


3. TRANSMISSION MODES at least 2 times the highest frequency contained in the signal.

1. The transmission of binary data across a link can be accomplished in either parallel or serial mode.

2. In parallel mode, multiple bits are sent with each clock tick.

3. In serial mode, 1 bit is sent with each clock tick.

4. there are three subclasses of serial transmission: asynchronous, synchronous, and isochronous.


Figure 4.31 at least 2 times the highest frequency contained in the signal.Data transmission and modes


4. DIGITAL-TO-ANALOG CONVERSION at least 2 times the highest frequency contained in the signal.

Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data.


Figure 5.1 at least 2 times the highest frequency contained in the signal.Digital-to-analog conversion


Figure 5.2 at least 2 times the highest frequency contained in the signal.Types of digital-to-analog conversion


  • Data element vs. signal element at least 2 times the highest frequency contained in the signal.

    • What is a signal element here?

  • 2. Bit rate is the number of bits per second.

  • 2. Baud rate is the number of signal elements per second. 3. In the analog transmission of digital data, the baud rate is less than or equal to the bit rate.

  • S = N x 1/r baud r = log2L


Figure 5.3 at least 2 times the highest frequency contained in the signal.Binary amplitude shift keying

B = (1+d) x S = (1+d) x N x 1/r


Figure 5.4 at least 2 times the highest frequency contained in the signal.Implementation of binary ASK


Figure 5.6 at least 2 times the highest frequency contained in the signal.Binary frequency shift keying


Figure 5.9 at least 2 times the highest frequency contained in the signal.Binary phase shift keying


Figure 5.12 at least 2 times the highest frequency contained in the signal.Concept of a constellation diagram


Figure 5.13 at least 2 times the highest frequency contained in the signal.Three constellation diagrams


Qam quadrature amplitude modulation
QAM – Quadrature Amplitude Modulation at least 2 times the highest frequency contained in the signal.

  • Modulation technique used in the cable/video networking world

  • Instead of a single signal change representing only 1 bps – multiple bits can be represented buy a single signal change

  • Combination of phase shifting and amplitude shifting (8 phases, 2 amplitudes)


Figure 5.14 at least 2 times the highest frequency contained in the signal.Constellation diagrams for some QAMs


5. ANALOG AND DIGITAL at least 2 times the highest frequency contained in the signal.

Analog-to-analog conversion is the representation of analog information by an analog signal.

Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us.

Example: radio stations


Figure 5.15 at least 2 times the highest frequency contained in the signal.Types of analog-to-analog modulation


Figure 5.16 at least 2 times the highest frequency contained in the signal.Amplitude modulation

The total bandwidth required for AM can be determined from the bandwidth of the audio signal: BAM = 2B.


Figure 5.17 at least 2 times the highest frequency contained in the signal.AM band allocation


Figure 5.18 at least 2 times the highest frequency contained in the signal.Frequency modulation


Figure 5.19 at least 2 times the highest frequency contained in the signal.FM band allocation

The total bandwidth required for FM can be determined from the bandwidth of the audio signal: BFM = 2(1 + β)B. β has a common value of 4


Figure 5.20 at least 2 times the highest frequency contained in the signal.Phase modulation

The total bandwidth required for PM can be determined from the bandwidth and maximum amplitude of the modulating signal:BPM = 2(1 + β)B.


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